A HISTORY OF DEVONSHIRE 



sandstones and marlstone bands are prevalent. In these thin bands 

 numerous pseudomorphs after rock salt were found at Windygate (the 

 cliff between Peak and High Peak Hills). In one of these beds Hutch- 

 inson* found numerous casts of equisetoid plants. 



In a boring put down near Lyme Regis in 1901 the Keuper Marls 

 were penetrated to a depth which may be estimated at about 1,130 feet, 

 without reaching their base. Jukes-Browne ' gives an abstract of their 

 succession as follows : — 



ft. in. 



Marls without gypsum 124 7 



Marls with veins of gypsum iiSio 



Clays with beds of gypsum 31310 



Gypsiferous marls with three beds of calcareous sandstone . 134 o 



Hard clays and marls with gypsum 297 7 



Hard silty and micaceous clays with some gypsum ... 140 5 



1,129 3 



Teall' attributes the prevailing colour of the New Red rocks 

 mainly to the (lateritic type of decomposition) ' subaerial decomposition 

 of rocks containing ferriferous compounds ' ' so common in tropical 

 regions of the present day.' ' Under this mode of decomposition the 

 iron becomes oxidized and deposited as a coating on the grains of quartz 

 and other undecomposed minerals. The red material thus produced would 

 mantle the slopes, fill up the hollows, or be spread out as flat fans over 

 the low ground by torrential action. It would also be deposited in lakes, 

 lagoons or seas. In the presence of decomposing organic matter the 

 ferric oxide would be reduced, the red colour would disappear, and the 

 iron would take the form of a sulphide or carbonate. Thus the change 

 in the colour seen near Axmouth at the junction of the Rhaetic and 

 Keuper was directly connected with the absence of fossils from the latter 

 and their abundance in the former deposit.' 



RHiETIC BEDS 



Owing to the Cretaceous overlap the Rhastic beds cannot be traced 

 continuously from the coast. They crop out, but are cut off by fault in 

 Pinhay Bay. Their main outcrop in Dowlands Cliff is largely concealed 

 by cretaceous debris from the landslip, but at Culverhole H. B. Wood- 

 ward* gives their thickness as 63 ft. 8 in., made up in descending order 

 of 15 feet of thin bedded white lias limestones based by an impersis- 

 tent bed of Cotham Stone, upon 18 feet of black shales containing 

 Avicula contorta, Cardium rhaticum, Pecten valoniensis, etc., with a bone 

 bed at their base containing Acrodus, Hybodus, etc. The succeeding 

 passage beds to the Keuper consist of 10 feet of green marl upon 20 

 feet of alternating pale greenish and cream-coloured marls with hard 



* P. O. Hutchinson, Trans. Devon Jsioc. vol. xi. p. 383. 



* ^art. Joum. Geol. Soe. May, 1902, p. 288. 



' Pm. Geol. Assoc. (1899), ^vi. pt. 3, pp. 141, 142 ; Exeter Memoir, 1902, p. 76. 



* Proc. Geol. Assoc, xvi. pt. 3, p. 135. 



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